1. Field of the Invention
The present invention relates to a golf ball with high moldability due to high resin flowability, good appearance, and high resilience.
2. Prior Art
A method of improving a cover material by adding an inorganic filler (titanium dioxide and barium sulfate) thereto has been proposed, for example, in Japanese Patent Laid-open No. Hei 6-277312. The addition of titanium dioxide and barium sulfate to the cover of a golf ball is effective to give excellent properties such as a carrying performance to the golf ball. With respect to the reason for this, the document describes that the addition of titanium dioxide and barium sulfate to the cover xe2x80x9cshifts a weight distribution in the ball from the core center to the cover side, to increase an inertia moment of the ball, thereby increasing the carry of the golf ballxe2x80x9d.
Such a proposal, however, has been required to be further improved in terms of factors determining golf ball performances, for example, a hardness factor of the cover and core, a composition factor of the cover and core, and a dimple factor. In particular, the ball disclosed in the embodiment of the above proposal has been required to be improved in terms of feeling of hitting the ball and the carry of the ball.
On the other hand, the properties of a golf ball strongly demanded by golf players are generally player""s soft feeling at the time of hitting the ball and the carrying performance of the ball; however, it is regarded as difficult to make both the properties compatible with each other for the following reasons:
(1) If the core is softened for ensuring the player""s soft feeling, a deformed amount of the hit ball becomes large, to degrade the durability against cracking.
(2) If both the core and cover are softened for ensuring both the player""s soft feeling and durability against cracking, the resilience and initial velocity of the ball are reduced, to sacrifice the carrying performance.
(3) If the ball is excessively improved only in terms of the player""s soft feeling, the other properties are sacrificed, to cause such an inconvenience that local deformation of the hit ball becomes large, not to keep the sphericalness of the ball at the initial stage of the carry of the ball, thereby degrading the carrying performance.
To solve the above problems, Japanese Patent Laid-open No. 2000-5341 has proposed an excellent golf ball characterized by combining a core, which is softened to improve the player""s soft feeling and durability against cracking, with a cover to which a reinforcement filler is added.
Such a golf ball, however, has been required to be further improved in terms of moldability, resilience, and appearance.
An object of the present invention is to provide a golf ball with high durability and very high resilience.
As a result of an examination made, by the present inventor, to achieve the above object, it has been found that a golf ball including a core, and a cover made from a cover material containing an ionomer resin and also barium sulfate and titanium dioxide added in a total amount ranging from 10 to 25 parts by mass on the basis of 100 parts by mass of the ionomer resin; wherein a flexural amount of the core, measured by applying a load of 980 N thereto, is in a range of 4.0 to 5.5 mm, a ratio of a melt-flow rate to a specific gravity (melt-flow rate/specific gravity) of the cover material is in a range of 1.6 or more, and a Shore D hardness of the cover is in a range of 55 to 65, is advantageous in improving the productivity and exhibiting excellent properties as described below by a synergistic effect of the above-described optimized requirements.
(1) Since the kind and the content of an inorganic filler are optimized, more specifically, since the content of the inorganic filler is specified not to be excessively large, it is possible to improve the durability, and to prevent degradation of the resilience (carrying performance) and lowering of moldability (resin flowability) and hence to improve productivity.
(2) Since barium sulfate and titanium dioxide are used in combination as the inorganic filler, a durability improving effect can be given by addition of barium sulfate and a disadvantage that the cover becomes yellowish by addition of barium sulfate is canceled out by addition of titanium dioxide. As a result, it is possible to improve the durability while ensuring a good appearance by preventing the cover from becoming yellowish.
The present inventor has further found that the productivity and performances of the above-described golf ball can be further improved by optimizing dimples of the golf ball and the adjusting the composition of the cover material as follows:
(3) If a ball is relatively soft, the spin of the hit ball becomes small, and therefor, if the ballistic path of the ball is excessively low, the carry of the ball may become insufficient because of the xe2x80x9cdropxe2x80x9d of the ball. To cope with such an inconvenience, the dimple total volume ratio (VR) is specified, to prevent the xe2x80x9cdropxe2x80x9d of the ball, thereby ensuring a high carrying performance.
(4) The resilience (carrying performance) can be further improved and thereby the carry of the ball can be made further longer by specifying the kind of the ionomer resin.
On the basis of the above-described knowledge, the present invention has been accomplished.
Accordingly, the present invention provides the following golf balls:
(1) A golf ball including; a core; and a cover made from a cover material containing an ionomer resin and also barium sulfate and titanium dioxide added in a total amount ranging from 10 to 25 parts by mass on the basis of 100 parts by mass of the ionomer resin; wherein a flexural amount of the core, measured by applying a load of 980 N thereto, is in a range of 4.0 to 5.5 mm; a ratio of a melt-flow rate to a specific gravity (melt-flow rate/specific gravity) of the cover material is in a range of 1.6 or more; and a Shore D hardness of the cover is in a range of 55 to 65.
(2) A golf ball according to claim 1, wherein a thickness of the cover is in a range of 1.0 to 2.0 mm.
(3) A golf ball according to claim 1 or 2, wherein a specific gravity of the cover material is in a range of 1.020 to 1.110.
(4) A golf ball according to any one of claims 1 to 3, wherein the golf ball has in the cover surface a large number of dimples; and a dimple total volume ratio (VR) is in a range of 0.85% or less, the dimple total volume ratio being defined as a ratio of a total volume of dimple spaces each of which is present under a plane surface surrounded by an edge portion of the dimple to a total volume of a virtual ball being the same as the golf ball except that the virtual ball has no dimples.
(5) A golf ball according to any one of claims 1 to 4, wherein the ionomer resin contains an Li-ion neutralized type ionomer resin and an Mg-ion neutralized type ionomer resin.
(6) A golf ball according to any one of claims 1 to 5, wherein the added amount of barium sulfate is larger than that of titanium dioxide.
(7) A golf ball according to any one of claims 1 to 6. wherein the cover material contains, on the basis of 100 parts by mass of the ionomer resin, 7 to 20 parts by mass of barium sulfate and 2 to 7 parts by mass of titanium dioxide.